It is important to a bicycle rider to have a seat that will remain comfortable despite either small or large bumps that may be encountered during the course of a ride.
A bicycle seat must be supported from the frame of the vehicle, the pertinent portion of which is generally in the form of a hollow tube. The assembly that supports the seat then consists mainly of two parts: an upper or inside post having its upper end fixedly attached to the seat; and a hollow lower or outside post that is inserted into the hollow frame member, and into whose upper end the upper post is then slidably inserted. The lower or outer post is fixed to the frame with regard to both rotation and vertical movement. The position of the upper post relative to the lower post is made adjustable, however, so that the seat can be placed at whatever height above the vehicle is most convenient for the rider.
It has been well known to utilize some kind of a spring support inside the lower or outer post in order to resiliently support the upper post and hence the rider. Previously known mechanisms have not been fully satisfactory, however.
What the rider needs to have beneath the bicycle seat is a suspension system that will provide firm support under normal conditions while riding on smooth surfaces, but which will drop downwardly whenever a large bump is encountered. If such vertical movement were not provided, the full impact of the bump would be transmitted to the rider's body as a sharp upward force.
The spring action occurs in three major phases, as follows: the pre-load, if any, which an initial load or force applied to the seat must overcome before any downward movement of the seat will take place; the spring strength, or the force of the spring action that resists the downward movement after it occurs; and the rebound characteristic, which includes both strength, speed, and smoothness of the upward return movement.
If the pre-load is too great it will cause the rider to feel that the support provided by the seat is stiff and uncomfortable.
If the pre-load is too small the seat will move down a large distance merely because the rider sits upon it. That will diminish the amount of downward travel that could later be available for absorbing vertical shocks.
If the spring strength is too great, too much of the force of a bump will be transmitted to the body of the rider.
If the spring strength is too small, the seat will bob up and down excessive distances in response to small bumps.
The rebound characteristic is also very important, because it can be either too fast or too slow for the comfort and convenience of the rider, and may also involve oscillatory movement, depending upon the type of spring system that is used.